The purpose of this project is to complete the isolation of the growth hormone dependent peptide, somatomedin, from human plasma and determine its primary amino acid composition. Its mechanism of production will be assessed by perfusing liver with growth hormone along with labeled amino acids. The relationship between somatomedin and other growth factors will be studied by determining their competition for insulin receptors in fat cells, lymphocytes, placentae, and chondrocytes. the ability of purified somatomedin to stimulate cell replication in vitro will be studied with human fibroblast and other cell cultures.